Edit a rotated object normally?
Change this value to "0", should reset it to flat.

Edit: option to leave it rotated normally, and edit at 0 degrees

If you add an empty, then set the object with a "copy rotation" constraint;



Then you can apply the rotation of the empty to the object, regardless of where they're located relative to each other.

Also, you can "hide" (disable) or "show" (enable) the rotation at-will with this icon here;